1. Field of the Invention
The invention relates to a piston for a piston/cylinder assembly in which a working piston fastened to a piston rod is arranged in a working cylinder filled with damping medium, wherein the piston is axially displaceable in the working cylinder and has damping valves for both the tension and compression directions of movement, each damping valve having a group of passage ducts which open on an outlet side at a control edge covered by valve disks.
2. Description of the Related Art
Pistons for hydraulic vibration dampers are already known, for example, from German Utility Model 19 41 188. In these known pistons, a piston body is fastened to a piston rod and has a group of passage ducts for each of the tension and compression directions of movement. Each group of passage ducts runs obliquely relative to the piston rod axis and opens on the outlet side into an annular groove forming a control edge and covered by valve disks. A problem with these prior art devices is that the obliquely running passage ducts cannot be produced together with the piston body because, for example, during sintering, the machining tools cannot be brought parallel to the piston rod axis. For this reason, the passage ducts must be produced in a further manufacturing operation such as, for example, by drilling or by a machining operation such as cutting if the cross sections are not a circular shape.
Other pistons for hydraulic telescopic vibration dampers are known, for example, from German reference DE-C 38 24 420 in which the inner radius of the inflow-side passage ducts is, starting from the piston rod axis, approximately as large as the outer radius of the outflow-side passage ducts. By virtue of this geometry, the passage ducts may be produced by noncutting machining operation, since, in each case, a part of the machining tool can penetrate axially in the direction of the piston rod axis from one end face of the piston body.
All damping systems are required to provide increasing degrees of comfort in vehicles. Comfort is influenced essentially by damping and friction. These comfort requirements, in combination with the required body damping, lead to precisely defined damping characteristic curves which are typically decreasing characteristic curves that have a compression/tension ratio in the lower speed range that does not correspond to the compression/tension ratio occurring at higher speeds. That is to say, the compression damping value at a first damping speed is higher than its corresponding value at a second damping speed and the tension damping value lower at the first damping speed than its corresponding value at the second damping speed. This relationaship has an adverse effect on comfort. To generate decreasing characteristic curves, relatively soft spring leaves or helical springs are highly prestressed so that they have high piston gradients. A problem with this solution is that the assemblies become rougher and therefore also louder. This roughness results primarily from the contact of the first spring leaf with the piston surface which occur at the higher speeds, higher forces and higher accelerations during opening and closing associated with highly prestressed springs.
For example, in known level-regulating systems such as disclosed in European Patent EP 0.867.317 Al there are no corresponding solutions, since these devices have large piston pin diameters along with relatively small piston diameters. The result of this configuration is that the area between the piston rod and the piston diameter comprises a small pressure-loaded surface and therefore requires high prestressing gradients to generate decreasing characteristic curves.